Limitation of IN clause in SQL

As far as I know, the SQL language itself has no limitation of this type. Various vendor database implementations might. Please check your database documentation (the answer will be buried somewhere, so keep looking).

I'm curious about the circumstances in which this question would arise. Presumably, you have either already encountered a limit in your database, and received an error message, or you are contemplating constructing a query which might, as they say, push the envelope.

This can happen when a dynamic query is constructed "on the fly" by an application program. For example, a program gathers userids from somewhere, then builds a list of these userids into an SQL statement like this:

select foo
     , bar
  from users
 where userid in
       ( 1, 3, 9, 37, 187, 845, 937, 1012, ... )

If this exceeds some database limit on IN lists (and I'm not suggesting such a limit exists), you may consider splitting the list in half:

select foo
     , bar
  from users
 where userid in
       ( 1, 3, 9, 37, 187, ... )
union all
       select foo
     , bar
  from users
 where userid in
       ( ..., 38248, 42482, 678937 )

However, that's not going to help if there's also a limit on the total number of characters that an SQL statement may comprise (and most databases have a limit on this, even if it's in the megabyte range), since the UNION statement will actually be a few characters longer.

What's the best solution if you do hit a limit? Consider doing it with a JOIN instead of an IN list.